This is a proposal to develop an effective immunotherapy of cancer by applying the thoracic duct fistula procedure in rats, thereby augmenting and modifying the immune response in order to obtain the greatest immune action against tumors. The fistula procedure modifies the immune response (a) by retaining in the circulation those components which are cytotoxic to the tumor, such as tumor sensitive lymphocytes and tumor cytotoxic antibodies, (b) by eliminating those components of the circulation which protect the tumor, such as IgG antibody, circulating tumor antigen which would neutralize and cytotoxic antibody or sensitive cell, and the complexes of IgG antibody and tumor antigen which have recently been implicated as blocking factor, and (c) by the reactivation of blocked lymphocytes. Thus the fistula procedure eliminates the feed back control and limitations of the immune system and will be studies with respect to its effect on tumor bearing rats and on the immune response of normal rats injected with antigens of known structure as well as that of tumor bearing rats. The various types of antibodies and sensitized cells produced during the immune response will be studied with regard to their class, homogeneity, specificity, rate of production and feedback control.